Solar water heating versus a heat pump for a Kenyan household

If your household showers with hot water heated by electricity, water heating is almost certainly the largest single item on your KPLC bill. An instant shower heater draws 3,000–4,500W; a storage geyser runs for hours a day. Nothing else in a normal home comes close.

That makes water heating the highest-return place to spend money on efficiency — often a better first investment than solar panels. There are two serious options.

How each one works

Solar water heating is a thermal system. Collectors on the roof absorb sunlight and heat water directly, which is stored in an insulated tank. There is no electricity involved in the heating itself — no panels, no inverter, no battery. Sunlight becomes hot water.

A heat pump is an electrical appliance that moves heat rather than creating it. It extracts warmth from the ambient air and concentrates it into the water tank, using a refrigeration cycle running in reverse. It uses electricity, but roughly a third to a quarter of what a resistive element would use for the same hot water.

Both remove most of your water-heating cost. They do it differently, and the difference decides which suits your house.

Solar water heating: the case for

No running cost at all. Once installed, the sun is free. There is no electricity input to the heating process.

Very few moving parts. A direct pressurised flat-plate system has essentially nothing to break — no compressor, no fan, no refrigerant. Longevity is excellent and maintenance is minimal.

Silent. Nothing runs, so nothing can be heard.

Well proven in Kenya. Solar water heating has been installed here for decades. Plumbers understand it, spares are available, and it is the technology most Kenyan installers know best.

Solar water heating: the case against

It needs roof space with sun. Collectors want a clear, well-oriented roof area. Shading is fatal to performance in a way it is not for a heat pump.

Overcast periods reduce output. A well-insulated tank holds heat for many hours, but several consecutive dull days will exhaust it. Most systems therefore include an electric backup element — which means on those days you are paying to heat water conventionally.

Output is fixed by the collector area. You cannot ask it to work harder because guests have arrived. Sizing must anticipate your peak household, not your average.

Flat plate or vacuum tube?

Two collector types, and the choice is more practical than technical.

Flat plate collectors are a glazed insulated box with an absorber plate. Robust, hail-tolerant, straightforward to maintain, and the standard choice for most of Kenya.

Vacuum tube collectors use evacuated glass tubes and reach higher temperatures in cooler or overcast conditions, which makes them attractive in the cool highlands — Nyahururu, Limuru, the Aberdares. The glass tubes are more fragile, and individual tubes can be replaced when broken.

For most of the country, flat plate is the sensible default. In consistently cool, cloudy highland areas, vacuum tubes earn their extra cost.

Heat pumps: the case for

They work regardless of sunshine. A heat pump extracts heat from air, and Kenyan ambient temperatures are favourable almost everywhere, almost all year. Rain and cloud barely affect it.

No roof space needed. The unit sits at ground level. For a house with a shaded roof, a roof already covered in solar panels, or a flat used for other purposes, this is decisive.

Consistent output on demand. It heats when asked, so a household with irregular hot-water demand is better served.

It pairs well with solar panels. Because a heat pump runs on electricity, a PV array can power it. Water is heated during the day, from your own generation, and stored — effectively using the tank as thermal storage instead of buying more battery.

Heat pumps: the case against

They use electricity. Far less than a resistive element, but not nothing. If your goal is to eliminate a cost rather than reduce it, solar thermal goes further.

Moving parts. A compressor and fan mean more that can fail, and more maintenance over the years than a flat-plate system.

Audible. The fan makes noise. Placement matters, especially near bedrooms or a neighbour's boundary.

Fewer local specialists. Heat pumps are newer in the Kenyan market than solar thermal. Servicing expertise is less widespread, which matters over a fifteen-year life.

Which suits your house

Choose solar water heating if you have unshaded roof space with reasonable orientation, your hot-water demand is fairly predictable, and you want the lowest possible running cost with minimal maintenance. This is most Kenyan houses.

Choose a heat pump if your roof is shaded, already fully committed to PV panels, or unsuitable structurally; if your hot-water demand is irregular; if you live somewhere persistently cool and overcast; or if you already have solar generation and would rather add a load you can shift into daylight hours than add more collectors.

Sizing, briefly

For solar water heating, size on household occupancy: 200 litres typically serves four to six people, 300 litres five to seven. Err upwards if guests are common — an undersized tank is a daily irritation, and the marginal cost of the next size up is small.

For a heat pump, size on tank volume and the recovery rate you need. A household that showers in a concentrated hour needs faster recovery than one spread across a morning.

Either way, insist that the tank is genuinely well insulated. Heat loss overnight from a poorly insulated tank quietly wastes a meaningful fraction of what either system produced.

The financial picture

The honest answer is that both pay back, and which pays back faster depends on your household's hot-water consumption, your tariff and the installed cost of each option at the time you buy.

What is not in doubt: either is a better first investment than PV panels for most households that heat water electrically, because the load being displaced is so large. If you can only afford one thing this year, and you currently heat water with electricity, this is usually where the money goes furthest.

What we supply

We stock pressurised flat-plate solar water heaters — see our water heating range — including the 300-litre direct pressurised system suitable for a household of five to seven, along with spares and controllers.

Pressurised matters: it gives you a proper shower flow rather than the weak gravity-fed trickle of older designs, and it works with the plumbing modern Kenyan houses are built with.

For heat pumps, tell us what you are trying to achieve and we will advise honestly on whether solar thermal, a heat pump, or a combination fits your house — including when the answer is that your existing setup is adequate and the money is better spent elsewhere.